From his post “Inside the Glass,’’ NBC analyst Pierre McGuire has perhaps the best seat in the house for the Stanley Cup Final between the Blackhawks and Bruins.

McGuire also has to go over the boards for pre- and postgame interviews with players on the ice, and in-game chats with coaches behind the bench. “Not every rink is like that,’’ he said. “Some, there’s doors in front of you or to the side, but in Boston and Chicago, you’ve got to go up and over.’’

It seemed fitting to McGuire that some things remained old school in this Original Six matchup, which shifts to Chicago for Game 5 Saturday night. “Just like the old times, yeah,’’ he said.

McGuire’s location gives him a perfect vantage point for the complexity and nuances of line changes, making the sport unique among the major professional leagues since it is the only one that allows personnel changes to be made on the fly.

Substitutions are allowed freely when play is stopped, but often they come as play continues. Because of the importance of matchups, especially in the playoffs, line changes become even more critical to avoid a penalty for too many men on the ice.

In this Cup Final, there have been four such penalties called already, the latest in the second period of Game 4 when Bruins defenseman Torey Krug was late getting off the ice during a change.

“I think line changes are so important at this part of the season. I don’t think I’ve seen so many too many men penalties in the Final, ever,’’ said Bruins forward Chris Kelly. “I don’t know if it’s a bad thing on both sides. There’s obviously line matching going on and you never want to get caught out too late. With three out of the four games having gone into overtime, the last thing you want to do is get caught out there, but things happen so quickly.”

Barry Melrose, the former Los Angeles Kings coach who is now an ESPN commentator, was amazed the too many men penalties have not resulted in a goal. “I don’t know if I’ve seen it twice in one game and I’ve seen that twice now — and it never hurt the team,’’ he said.

In the NHL, teams typically deploy four lines and three pairs of defensemen. Players usually skate in shifts lasting 30-35 seconds.

NHL rules stipulate that players cannot hit the ice until the ones they are replacing get within 5 feet of the bench. The preferred method is to have players leaving the ice enter the bench through a door furthest from the puck. Players entering the game, meanwhile, hop over the wall at the end of the bench nearest the puck, which minimizes the potential for a risky change by allowing defensemen to remain on the rush and prevent the forwards from being out of position on the forecheck.

“It’s fascinating, actually, and it makes you appreciate the talent of the players and the hard work of the coaches through film study in creating their matchups,’’ Maguire said. “It just shows you how precise the game is, because sometimes it can look like chaos, but it’s not. It’s really organized, and it’s really structured.’’

“The coaches would roll three or four lines in, and the rule of thumb was to change when you got to the red line, at the time, and dump it in on the bench side, because in order to transit the puck back up the ice, they’d have to go far side again,” he said. “Often, there would be one guy who would stay a little longer to slow the play down and allow for the line change and make it as quickly as possible. But the rule of thumb is to change when the puck was being dumped into the zone.

“That’s changed dramatically. It’s changed, first of all, because the shifts have gone to 30-35 seconds, so you have exponentially more line changes, and the matchups that the coaches want are so disciplined that that requires more line changes and it requires people on the bench to stay much more attentive and much more alert and ready to go.
Those things really complicate matters.’’

In the modern game, line changes are often dictated by matchups, such as in the Bruins’ playoff series against Toronto when Maple Leafs coach Randy Carlyle tried to get high-scoring forward Phil Kessel away from Bruins defenseman Zdeno Chara.

Every time Kessel rolled over the boards, Bruins coach Claude Julien instructed assistant Doug Houda, who monitors the minutes and matchups of his defensemen, to make certain Chara and sidekick Dennis Seidenberg were on the ice.

“They’re constantly trying to change and those changes end up right in front of me,’’ McGuire said. “But one thing I can tell you, in Game 1 when it went to three overtimes and Chicago took two too many men on the ice penalties, the Bruins players, to a man, when the coaches would tell them, ‘Chara, you’re up; Seidenberg, you’re up,’ then Chara would say, ‘I have [Andrew] Ference,’ and Seidenberg would say, ‘I have [Johnny] Boychuk,’ so they would make sure it was a double reinforcement.’’

The players engage in a system of redundant communication before taking the ice to avoid a penalty for too many men on the ice.

“It’s incumbent upon the players to have communication with one another,’’ said NESN analyst Andy Brickley. “It’s the coach who directs what players and what line is up next to be ready for the line change, so it is complex.’’

When an opponent tries to manipulate its lines, it can complicate matters for the team trying to make a corresponding line change, which proved to be the case in Boston’s most infamous too many men penalty in the 1979 Stanley Cup semifinals against the Canadiens.

“It was the double shifting of Don Marcotte, and [Guy] Lafleur stayed out for 2½ to 3 shifts,’’ recalled Milbury, who was a Bruins defenseman on the ice for that fateful shift that resulted in a penalty, and Lafleur’s tying power-play goal with 1:14 left. Yvon Lambert struck for the game-winner at 9:33 of overtime. The Canadiens went on to beat the Rangers in five games to win the Cup.

“The left wingers on that line, somebody should have skipped a line, but [Marcotte’s] line was up and he was supposed to go and there was confusion as to which left winger should replace Marcotte, and therein lied the problem,’’ Milbury said. “But the root of the problem was that Lafleur was triple shifting, and we got caught.’’

So, when does a player know his shift is over and it is time to skate off the ice?

“There’s an internal clock and you know you’ve been out for whatever length of time, and there develops an odd-man rush and that’s obviously not a time to change,’’ Milbury said. “But if there develops a situation where you’ve made a rush back and forth, up and down the ice, two or three times and there’s nothing going on and your linemate dumps it in, then it’s an obvious time to change. It’s much better to be caught short than to be caught long.’’

There is another important aspect of line changes that often goes overlooked and unappreciated by the casual observer.

“Puck possession matters so much because you never want your players to get out of the rhythm or the flow of the game, so faceoff play becomes so important,” said McGuire. “If you look at Game 3, Boston dominated faceoffs, they dominated the flow of the game, and they got a shutout in the game.”

Said Melrose, “To run a bench, it’s very important, and you’ve got to make sure you have the right guys on the ice. A coach’s biggest fear is if I get caught with my fourth line against their first and they end up scoring the winning goal and I’ve got the wrong guys on the ice.’’

Julien said he is the final arbiter on all matters pertaining to line changes and matchups.

“The responsibility is mine,” he said. “I don’t think we’ve ever been caught with too many men on the ice because I’ve called four guys up front instead of three, OK, because I know how to count. But it has happened when somebody’s daydreaming at the other end of the bench, and my arm is not long enough to pull him back in.’’

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